Hydrocarbon-containing fluids are widely used as solvents, for example in adhesives, cleaning liquids, explosives, solvents for decorative coatings, paints and printing inks, light oils used in applications such as metal extraction, metal working or mould release, industrial lubricants and drilling fluids. Hydrocarbon-containing fluids can also be used as dilution oils in adhesives and sealing systems such as silicone mastics, as viscosity reducers in formulations based on plasticized polyvinyl chloride, as solvents in polymer formulations serving as flocculants, for example in water treatment, mining operations or paper manufacture and also as thickeners in printing pastes. Hydrocarbon-containing fluids can moreover be used as solvents in a very wide range of other applications, for example in chemical reactions.
In order to produce these hydrocarbon-containing fluids, the petroleum cuts used as feedstocks are treated in hydrodearomatization units by a process of catalytic hydrogenation composed of several reactors in series operated at high pressure. These reactors have one or more catalytic beds. The units are composed of main treatment sections which are generally: the feedstock storage unit, the hydrogenation section with several reactors, the distillates separation section and the distillation column (see FIG. 10).
The configuration generally put in place for the hydrogenation section is a sequence of several reactors in series. The efficiency of the hydrodearomatization by hydrogenation unit is dependent on several parameters and particularly on the level of catalytic activity of the first reactor used as a sulphur trap. This activity decreases with time until it becomes zero after a complete period of use. The catalytic activity depends on the quantity of sulphur supplied to the surface of the catalyst by the feedstocks to be treated. The quantity of sulphur captured by the catalyst of the first reactor is directly proportional to the sulphur concentration of the petroleum feedstock. Thus very little sulphur arrives at the second and third reactor in the series.
Sulphur is a poison to the catalyst necessary for the dearomatization reaction, and the aromatic compounds must be hydrogenated in order to obtain high-purity products. The catalyst of the first reactor used as a sulphur trap is therefore rapidly saturated by the quantity of sulphur supplied with the feedstocks to be treated. It is then necessary to change the catalyst of this first reactor. Furthermore, in order to avoid a spillover of sulphur into the second reactor, the catalyst of the first reactor will be changed at a maximum saturation of 90% and not 100%, thus resulting in reduced profitability. By contrast, as the second and third reactors receive only a little sulphur; their catalyst will be replaced only after longer cycles of treatment which may last up to several years. Current configurations of the hydrodearomatization units require a complete shutdown of the entire unit in order to change the catalyst, even if only the reactor 1 is involved. This complete shutdown of the units involves a considerable loss of production, as the shutdown may last several days.
An objective of the application is to provide an improved dearomatization process for the continuous preparation of hydrocarbon-containing fluids. Another objective of the invention is to provide a system for the optimized treatment of petroleum feedstocks allowing a reduction in production losses and flexibility of operability. The invention also has the objective of allowing complete saturation of the hydrogenation catalysts of the hydrodearomatization process before unloading.